Our host has said we're set-up for SSL and all he needs to do is 'push a button'. Essentially, forcing the HTACCESS to force users onto the HTTPS.
I remember reading about the change to HTTPS a while back and if I remember right, it was a damn sight more complicated than this.
But we're running wordpress, so maybe it is just that simple?
I'm assuming we would not need to take any further action? i.e. notifying Google etc? And our rankings would remain what they are now (if not better) with no drop in traffic?